Dust separator



Search Room March 22, 1938. c. H. w. CHELTNAM DUST SEPARATOR Filefifune 24.

INVENTOK. M m. 1am

2 Sheets-Sheet 1 rron/vs r.

OUdI UH nuum 183. GAS SEPARATE Much 22, 1938. c. H. w. CHELTNAM 2,111,754

DUST SEPARATOR Filed June 24. 1936 2 Sheets-Sheet 2 FIG. 4

FIG. 6

' INVENTIJR firmer,

Patented Mar. 22, 1938 DUST SEPARATOR Charles Henry Wood Cheltnam, Brockley, London, England Application June 24, 1936, Serial No. 86,978 In Great Britain June 27, 1935 7 Claims.

This invention relates to centrifugal dust separators of the kind comprising a separating chamber of approximately circular cross-section (i. e., of circular or scroll shaped cross-section) into which dust ladened gas (hereinafter referred to as air) is propelled tangentially through a rectangular inlet passage extending substantially the full length of the chamber and from which the major portion of the air, more or less dust free, passes either tangentially through an air port in the side of or axially into an open end in a central discharge pipe, and from which the minor portion of the air, which contains most of the dust, may be shunted to a comparatively small cyclonic separator and precipitator. Separators of this kind are employed where large volumes of air or gas are to have only the coarse dust particles removed and have a high volumetric efiiciency. In some cases, the central discharge pipe for the cleaned gas may be a chimney or smoke stack.

It can be demonstrated by experiment with smoky gases that when a fluid passes round a bend in a duct of square or rectangular section, two vortices are formed, the cross-sectional area of the duct being divided equally between them. The direction of the vortical motion is approxi mately at right angles to the main stream, and the direction of rotation is such that the flow of the fluid adjacent to the flat sides of the bend is from the outer to the inner curved surface 01 the bend. If the bend is extended through an angle of 360 degrees so as to form a hollow circular prism comprising an inner and an outer cylinder and two annular ends, assuming that the motion of the main stream is maintained, the two vortices become two vortex-rings rotating in opposite directions in any longitudinal section and gearing together at their adjacent surfaces. The reason for these phenomena is the pressure gradient within the vessel, the pressure being greatest adjacent the outer walls the viscosity of the fluid acting in such a way that a fiow of fluid from a region of high to a region of low pressure takes place adjacent to the surface of each of the two ends of the vessel. The

matter is more fully explained in an article entitled Experiments on Streamline Motion in Curved Pipes by Prof. John Eustice in the Proceedings of The Royal Society of London. A. Vol. 85 (1911 on page 119, and also in an article entitled Note on the Motion of Fluid in a Curved Pipe by W. R. Dean, M. A. in the Philosophical Magazine, Vol. 4. (July-December 1927) on page 208.

In separators of the kind specified, the main ingoing stream of dust laden gas is divided into two vortex rings, in the manner above described. In the case where the cleaned gas passes tangentially through a port in the side of the d scharge pipe each of the vortex rings evacuates itself independently of the other into the said pipe, each half of the gas passing through one vortex ring only; while in the case where the cleaned gas passes axially into an open ended eduction pipe about half of the gas will pass through the vortex ring adjacent that end of the vessel in which is situated the said pipe and the whole of the gas will pass through at least a part of the other vortex ring, the first mentioned ring evacuating into the second which evacuates the whole.

In separators of the kind specified, it has previously been proposed to shunt the concentrated dust laden air from the separating chamber either through a longitudinal dust port in the side wall or through radial dust ports in the end walls, said dust ports being situated some distance round the separating chamber from the inlet. In these previously proposed arrangements, owing to the relatively high velocity of the secondary motions at the periphery of the vortex rings, compared with the primary motion, in all parts except in a portion of the first quadrant of the separator, a large portion of the finer dust cannot be caught in longitudinal or radial dust ports and is swept into the central discharge pipe and some of the coarser dust cannot reach the said dust ports, and the separation efiiciency of the apparatus is thereby reduced. The present invention is directed towards increasing the separation efliciency, whilst retaining the high volumetric efficiency of this kind of separator.

In a separator of the kind specified, according to the present invention, a circumferential dust port is provided atone or each end of the separating chamber and extends around at least a part of the circumference'from a point near enough to the inlet to ensure that the dust is swept through the dust port or ports by the secondary motions before it can be swept into the central discharge pipe. By circumferential dust port is meant a dust port the circumferential dimension of which is substantially greater than the other dimension.

Preferably the said port is formed in the end wall adjacent the periphery thereof and extends over at least half the circumference.

The air and dust passing through the dust port or ports may be shunted to a secondary separating chamber and a suction fan arranged to draw air through the primary or both separating chambers and the said discharge pipe provided with adjustable dampers for adjusting the proportion of air shunted to the secondary separating chamber the object being to maintain the overall separation efilciency, ii and when the total volume of air to be cleaned is reduced, by compelling a greater proportion of the air to be shunted with the dust.

When a suction fan is used for drawing the air into the primary separating chamber antiwhirl vanes may be arranged to convert the whirling motion of the air to an axial motion prior to its entry into the fan.

The invention will now be described, by way of example, with reference to the accompanying drawings. Fig. 1 shows one form of the dust separator in side elevation and partly in section on the line I--I of Fig. 2, Fig. 2 is a section on the line 11-11 of Fig. 1 with lower part of scroll chamber broken away, Fig. 3 is a top or plan view, Fig. 4 shows a modified form of separator in side elevation partially broken away and shown in section; Fig. 5 is a section on the line VV of Fig. 4 and Fig. 6 is a top or plan view of Fig. 4. Certain parts which are hidden from view are shown in broken line.

With reference to Figs. 1, 2 and 3, a primary separating chamber I of scroll shaped cross-section is provided with a rectangular tangential inlet passage 2 extending the whole length of the chamber. A circular discharge pipe 4 having an open end 5 extends axially into the chamber I through the end plate 3. The opposite end plate 6 is formed with a dust port consisting of a circumferential slot 1 extending from a point adjacent the inlet 2 over the major portion of the circumference.

A number of anti-whirl vanes 8 are arranged in the open end 5 of the pipe 4. Further within the pipe are arranged a pair of balanced dampers 9 mounted on spindles I0. These spindles extend through the side of the pipe 4 to enable the dampers to be operated from without to vary the size of the air passage through the pipe. The pipe 4 leads into the casing II of a suction fan.

The dust together with a small quantity of air is shunted from the primary separating chamber into a secondary separating chamber I2. This chamber I2 has a dirty air inlet I3, a clean air outlet I4 and a dust outlet I5 and constitutes a separate small cyclonic separator of the type described in British patent specification No. 406,036. The dust outlet l5 leads into a dust hopper IS. A duct I'I connects the dust port I to the inlet l3. A duct I8 connects the outlet I4 to the pipe 4 by means of the surrounding chamber 2I.

In operation the suction fan in the casing II draws air through the pipe 4 and so draws the dust laden air into the chamber I through the tangential inlet passage 2. Owing to the tangential entry of the dust laden air, it is given a primary motion around the chamber I. In addition to this primary motion a secondary motion is set up and results in the formation of two vortex rings in the manner described above. The dust moves to the wall of the separating chamber under the influence of its superior centrifugal force and it will be seen that the slot I is situated so that the secondary motion assists in sweeping the dust on or near the wall through the slot 1. As the velocities imparted to the dust particles by the secondary motion is far greater than that imparted by the primary motion, the positioning of the slot in this manner leads to greater efficiency than in the case of a longitudinal dust port extending along the side of the chamber and through which the dust particles are directed almost entirely by the primary motion because in the latter case some of the dust will be carried centripetally onto the end wall and into the clean air outlet before it can pass suificiently round the separating chamber to reach the iongitudinal dust port. The secondary motion serves also to direct the air, after it has. been.

freed of at any rate the major portion of its dust,

into the open end 5 of the pipe 4, whence it is drawn by the fan and discharged into a chimney or other outlet. As this air enters the pipe 4 its whirling motion is converted by the vanes 9, so that the flow of air into the fan is almost wholly axial and the efilciency of the fan is thereby increased. In addition to drawing air from the chamber I, the fan also serves to draw air through the duct I8 and hence draws the dust which passes through the port I, together with a small portion of air, through the duct I1 into the secondary separating chamber I2. Here the air is freed of its dust, which falls through the outlet I5 into the hopper I6, and the clean air drawn through the duct l8 into the pipe 4, whence it is delivered to the chimney or other outlet along with the clear air from. the chamber I.

The proportion of air which is shunted into the secondary separating chamber may be adjusted by means of the dampers 9. By closing the dampers 9, the resistance through the primary separator is increased and thus more air is caused to flow through the secondary separator and vice versa.

It will be seen that the vanes 8 do not extend to the middle of the pipe 4. This is because there is a natural inert core passing axially through the centre of the chamber.

In the modified construction shown in Figs. 4, 5 and 6, similar reference numerals are used to denote parts corresponding to those in Figs. 1, 2 and 3. In this construction the discharge pipe 4 is not open ended, but extends through the chamber I from end to end, and is provided in its side with a. rectangular port I9. This port is situated so that air entering through the passsage 2 can only reach the port after passing most of the way round the chamber.

The adjustable dampers 9 are now fitted in this rectangular port. A further difference is that a circumferential dust port I is formed in the end wall 3 as well as in the end wall 6, the two ports being connected to the duct II by two separate ducts 20. In this case each dust port 1 extends over approximately half the circumference from a point removed from the inlet by about one quadrant.

In operation dust is discharged from the chamber I through both dust ports I. Since the air cannot reach the port I9 until it has passed through at least two quadrants, the beginning of the ports 1 can be further removed from the inlet than in the first construction. Consequently the dust particles have become more accumulated on the wall of the separating chamber and the secondary motions have reached a greater velocity by the time they reach the dust port, than they do in the first construction. The clean air is directed into the port I9 by the primary mo- "all point remote in the direction of gas flow from that at which said inlet passage enters said chamber, and each end of said chamber being provided with a circumferential dust port adjacent the periphery and extending around at least a part of the circumference thereof from a point near that at which said inlet passage enters said chamher, and means for causing the dirty gas to pass through said inlet passage into said chamber.

2. A centrifugal dust separator comprising a primary separating chamber of approximately circular crosssection, a dirty gas inlet passage of rectangular cross-section leading tangentially into the side of said chamber and extending substantially the full length thereof, a clean gas discharge pipe extending axially within said chamber, at least one end of said chamber being provided with a circumferential dust port adjacent the periphery of said end and extending around at least a part of the circumference thereof from a point near that at which said inlet passage enters said chamber, a. secondary sepa rating chamber, said secondary separating chamber having a dirty gas inlet, a clean gas outlet and a dust outlet and constituting a separate small cyclonic separator, a duct connecting said dust port to the dirty gas inlet of said secondary separating chamber, a duct connecting the clean gas outlet of said secondary separating chamber to said clean gas discharge pipe of the primary separating chamber, and a suction fan to the inlet side of which said clean gas discharge pipe is connected, said fan serving to draw gas through both separating chambers. 3. A centrifugal dust separator comprising a separating chamber of approximately circular cross-section, a dirty gas inlet passage of rectangular cross-section leading tangentially into the side of said chamber and extending substantially the full length thereof, a clean gas discharge pipe extending axially within said chamber, at least one end of said chamber being provided adjacent its periphery with a dust port of narrow radial width and extending circumferentially over at least half the peripheral circumference of said end from a point near where said inlet passage enters said chamber, and means for causing the dirty gas to enter through said inlet passage into said chamber and to discharge clean gas through said axial discharge pipe, said means causing discharge of separated dust and residual dirty gas through said dust port.

4. A centrifugal dust separator as claimed in claim 2 comprising in addition adjustable dampers in said clean gas discharge pipe, said dampers serving to adjust the proportion of gas shunted to said secondary separating chamber.

5. A centrifugal dust separator comprising a separating chamber of approximately circular cross-section, a dirty gas inlet passage of rectangular cross-section leading tangentially into the side of said chamber and extending substantially the full length thereof, a clean gas discharge pipe extending axially within said chamber, at least one end. of said chamber being provided with a circumferential dust port adjacent the periphery of said end and extending around at least a part of the circumference thereof from a point near where said inlet passage enters said chamber, a suction fan attached to the discharge 0 side of said clean gas discharge pipe, said fan serving to draw the dirty gas into the separating chamber through said dirty gas inlet passage OBHFCH and draw the separated clean gas through said clean gas discharge pipe, and vanes arranged HOOm within said clean gas discharge pipe for destroying whirling motion of the clean gas before it enters the suction fan.

6. A centrifugal dust separator comprising a separating chamber of approximately circular cross-section provided with end walls, an inlet passage for dust laden gas of rectangular crosssection leading tangentially into the side of said chamber and extending substantially from one end wall to the other, a discharge pipe for cleaned gas located axially within said chamber and extending through at least one of said end walls, pressure means for causing a current of dust laden gas to enter the chamber through said inlet passage and by deflection of the circular wall of said chamber follow a curved path between said discharge pipe and the inner periphery of the chamber and thereafter discharge as clean gas through said axial discharge pipe, the curved path of movement of the current of gas in following the inner periphery of the chamber being adapted to develop vortex rings in said current of gas in the space between said end walls, said vortex rings being effective to carry the dust radially outward and then substantially transversely of the inner periphery of said chamber and toward said end walls, and a radially narrow circular slot-like dust discharge opening extending substantially half the circumference in at least one of said end walls, one edge of said discharge opening being coincident with the inner periphery of said chamber, through which the dust carried by said vortex rings is ejected and a circumferentially disposed conduit covering said slot-like discharge opening.

7. A centrifugal dust separator comprising a separating chamber of approximately circular cross-section provided with end walls, an inlet passage for dust laden gas of rectangular crosssection leading tangentially into the side of said chamber and extending substantially from one end wall to the other, a discharge pipe located axially of said chamber and passing through one end wall thereof, the inner end of the pipe opening within the chamber and the outer end thereof being provided with suction means for causing a current of dust laden gas to enter the chamber through said inlet passage and by deflection of the circular wall of the chamber follow a curved path between said discharge pipe and the inner periphery of the chamber and thereafter discharge as clean gas through said axial discharge pipe, the curved path of movement of the current of gas in: following the inner periphery of the chamber being adapted to develop vortex rings in said gas current in the space between said end walls, said vortex rings being effective to carry the dust radially outward and then substantially transversely of the inner periphery of said chamber and toward said end walls, a radially narrow circular slot-like dust discharge opening extending substantially half the circumference in the end wall of the chamber, said discharge opening having one edge coincident with the inner periphery of said chamber, through which the dust carried by said vortex rings is ejected and a circumferentially disposed conduit over and cooperating with piping connections from said dust discharge opening for utilizing said suction means for carrying away the dust discharged from said opening.

CHARLES HENRY WOOD CHEL'I'NAM. 

